1. Field of the Invention
The present invention relates to an apparatus for controlling a continuously variable transmission (CVT) used in a vehicle.
2. Description of the Prior Art
A CVT capable of continuously controlling a speed ratio e (=output side rotational speed/input side rotational speed) is used in a vehicle for a power transmission unit with excellent specific fuel consumption. A desired engine speed Ne' is set as an engine speed to achieve an output horse power of the engine set as a function of a pedalling amount of an accelerator pedal for example with a minimum fuel consumption, and the CVT is controlled such that an actual engine speed Ne is equalized to the desired engine speed Ne'. In the prior method of controlling the CVT, the speed change of the CVT, i.e. the alteration in the speed ratio e is always effected when there is some deviation between Ne and Ne', while the transmission loss of the CVT during the speed change is so large drive torque is disadvantageously transmitted. Thus, when the vehicle is accelerated, the acceleration performance may be improved and advantages may be provided in the specific fuel consumption by elongating a period of time when the engine speed Ne having small transmission loss of the CVT is low to increase the drive torque rather than by increasing rapidly the engine speed Ne to the desired engine speed Ne' through the speed change of the CVT.